Magnetic Resonance Imaging (MRI)

The magnetic fields and radiofrequency waves themselves are imperceptible to the patient, and no harmful effects from them have been documented. The contrast agent used for many MRI studies, however, does carry considerations. MRI contrast is gadolinium based, not the iodinated contrast used in CT. The FDA warns that small amounts of gadolinium can be retained in the body, including the brain, for months to years, and requires a class warning on all gadolinium agents (FDA). In patients with severe kidney impairment (generally an eGFR under 30), gadolinium is linked to nephrogenic systemic fibrosis, so renal function is screened before contrast is given (ACR Manual on Contrast Media).

Procedure

The exact protocol varies by body area, but the general flow is:

1. If indicated, start an IV line to give contrast medium before the scan.
2. Position the patient supine on a narrow, padded, nonmetallic table that slides into the scanner.
3. Tell the patient to hold still.
4. Radiofrequency energy is directed at the target area. The radiologist may vary the waves and use the computer to manipulate and enhance the images.
5. Images display on a monitor and are recorded on film or magnetic tape for permanent storage.
6. Have the patient keep the eyes closed to aid relaxation and reduce the closedin feeling.
7. If claustrophobia triggers nausea, coach the patient to take deep breaths.
8. If the scan runs long with the patient lying flat, watch for orthostatic hypotension.

Types

• Abdominal and pelvic
• Blood vessels (magnetic resonance angiography)
• Breast
• Cardiac
• Intracranial
• Musculoskeletal
• Spinal
• Urinary tract

Contraindications

• Severe obesity (usually more than 300 pounds)
• Claustrophobia
• Confusion or agitation
• Instability requiring continuous lifesupport equipment, since most monitoring equipment cannot run inside the scanner room (magnet-adaptive equipment is becoming available)
• Implantable metal objects such as pacemakers, infusion pumps, aneurysm clips, inner ear implants, and metal fragments in one or both eyes, because the magnet can move the object and injure the patient

Interfering Factors

• Inability to remain still during the scan
• Inability to fit into the scanner

Nursing Responsibilities

Before the procedure

• Explain the purpose of the test, who performs it, and where it happens.
• Tell the patient he will lie flat on a narrow bed that slides into a large cylinder housing the MRI magnets. Warn him about the clicking, whirring, and thumping noises and offer earplugs.
• Explain that MRI is painless and the scanner involves no radiation. A contrast dye may be used depending on the tissue studied.
• For MRI of the urinary tract, have the patient avoid alcohol, caffeine-containing beverages, and smoking for at least 2 hours and food for at least 1 hour before the test. Medications can continue except iron, which interferes with imaging.
• Tell the patient he must stay still for the entire procedure.
• For the claustrophobic or anxious patient, explain that a mild sedative is available, or that an open MRI scanner (slower but less confining) may be used. He can talk to the technician throughout, and the scan stops if he feels claustrophobic.
• If gadolinium contrast will be used, get an allergy and hypersensitivity history and check renal function (eGFR), since severe kidney impairment raises the risk of nephrogenic systemic fibrosis. Flag any sensitivities on the chart and notify the provider.
• Have the patient remove all metallic objects: jewelry, hairpins, watches.
• Ask about implanted metal devices or prostheses (vascular clips, shrapnel, pacemakers, joint implants, filters, intrauterine devices). Any of these may rule out the test.
• Confirm the patient or a responsible family member has signed informed consent.
• Give the prescribed sedative if ordered.
• At the scanner room door, recheck the patient one last time for metal.
• Just before the scan, have the patient void.

During the procedure

• Remind the patient to stay still.
• Assess how the patient tolerates the enclosed space and reassure as needed.
• Monitor cardiac function for ischemia (chest pressure, shortness of breath, hemodynamic changes).
• If the patient is unstable, confirm the IV line has no metal components and all equipment is MRI compatible. Monitor oxygen saturation, cardiac rhythm, and respiratory status as needed. A heavily sedated patient may need an anesthesiologist.

After the procedure

• Tell the patient he may resume usual activities as ordered.
• If the scan ran long and the patient was flat for an extended period, watch for orthostatic hypotension.
• Provide comfort measures and pain medication as needed for the prolonged positioning.
• Monitor for adverse reaction to the contrast medium (flushing, nausea, urticaria, sneezing).

Normal Results

• Findings depend on the specific type of MRI
• Structure and function of the studied organ within normal parameters for the patient

Abnormal Results

• Findings depend on the specific type of MRI
• Abnormalities depend on the particular organ studied

Frequently Asked Questions

Why can't some patients with metal implants have an MRI?

The strong magnet can move or heat ferromagnetic objects, which can injure the patient or damage a device. Pacemakers, infusion pumps, aneurysm clips, inner ear implants, and metal fragments in the eye are classic contraindications. Patients are screened at scheduling and rechecked for metal at the scanner room door, and many newer devices are MRI conditional and need their specific safety conditions confirmed first.

Is MRI safe? Does it use radiation?

MRI uses a magnetic field and radiofrequency waves, not ionizing radiation, so there is no radiation exposure. The magnetic field and radio waves are not felt, and no harmful effects from them have been documented. The main safety concerns are metal objects in the magnetic field and, when used, the gadolinium contrast agent.

Is the gadolinium contrast used in MRI safe?

For most patients it is well tolerated. The FDA notes that trace gadolinium can be retained in the body for months to years and requires a warning on all gadolinium agents, though retention has not been tied to harm in people with normal kidneys (FDA). In severe kidney impairment it is linked to nephrogenic systemic fibrosis, so renal function is checked first (ACR Manual on Contrast Media).

What can be done for a claustrophobic patient?

A mild sedative can be ordered, or an open MRI scanner (slower but less confining) can be used. Coaching the patient to keep the eyes closed and breathe deeply helps, and the patient can talk to the technician throughout, with the scan stopped if claustrophobia becomes overwhelming.

Why is the patient told to hold still?

Movement during the scan blurs the images and makes them unreliable, which can force the study to be repeated. The patient is reminded to stay still throughout, and is warned ahead of time about the loud clicking, whirring, and thumping noises so they are not startled into moving.

Does the patient need to prepare for an MRI?

Most MRI studies need no special preparation beyond removing all metal objects and clothing with metal. For an MRI of the urinary tract, the patient avoids alcohol, caffeine, and smoking for at least 2 hours and food for at least 1 hour beforehand, and holds iron supplements, which interfere with imaging.